"I'm working on [a new novel], and a number of 'Ice and Fire'-related things at the same time," he explained in an official HBO interview.

"Not only 'The Winds of Winter', which is Book 6, but we're also coming out with a big concordance called 'The World of Ice and Fire', which is about the whole history of Westeros and will be lavishly illustrated."

The author explained that, with his multitude of projects, "production [on the TV series] is moving faster than I can write".

"It's a slow process the way I write, especially books of this size that are as large and complex as they are," he said. "It's still a slow process.

"I am aware of the TV series moving along behind me like a giant locomotive, and I know I need to lay the track more quickly, perhaps, because the locomotive is soon going to be bearing down on me."

Martin added that he hopes his novel series and HBO's show will ultimately conclude simultaneously.

"The last thing I want is for the TV series to catch up with me," he said. "I've got a considerable headstart, but production is moving faster than I can write. I'm hoping that we'll finish the story at about the same time."